Vision systems that perform measurement, inspection, alignment of objects and/or decoding of symbology (e.g. bar codes) are used in a wide range of applications and industries. These systems are based around the use of an image sensor, which acquires images (typically grayscale or color, and in one, two or three dimensions) of the subject or object, and processes these acquired images using an on-board or remote, interconnected vision system processor. The processor generally includes both processing hardware and non-transitory computer-readable program instructions that perform one or more vision system processes to generate a desired output based upon the image's processed information. This image information is typically provided within an array of image pixels each having various colors and/or intensities. In the example of a symbology (barcode) reader, the user or automated process acquires an image of an object that is believed to contain one or more barcodes. The image is processed to identify barcode features, which are then decoded by a decoding process and/or processor obtain the inherent alphanumeric data represented by the code. In other types of vision systems, various vision system tools (e.g. edge detectors, calipers, blob analysis) are employed by the system processor to detect edges and other features that allow for recognition of object features, and the determination of desired information based upon these features—for example whether the object is defective or whether it is properly aligned.
It is increasingly desirable to provide vision systems and associated vision system components that can be used for a variety of purposes. In any vision system, a key component is the vision system camera assembly. The camera assembly includes a lens (optics) and an imager (or “sensor”) that provides the array of image pixel information. The vision system processor, as described above, receives the pixel data from the imager/sensor and processes it to derive useful vision system information about the imaged scene and/or object. The vision system processor and related components (e.g. data memory, decoders, etc.) can be provided within the camera assembly's housing or enclosure, or some or all of these components can be mounted remotely (e.g. within a PC, or other remote, self-contained processing system), and linked by a wired or wireless interconnect. Likewise, the camera assembly can include an on-board ring illuminator surrounding the lens, and/or another illumination arrangement that provides light to the imaged scene.
To increase the versatility of a vision system camera it can be desirable to employ differing types of lenses with a single camera assembly housing. In this manner, the user can tailor the optics to the particular vision system task. For example, some tasks can benefit by the use of a larger lens, such as a cine or C-mount unit (1-inch/25.4 mm in nominal base diameter), while others can be accomplished best with a smaller M12 thread (12 min×0.5 mm thread) lens, also termed an “S-mount”, or more basically, an “M12” lens. Others are best suited to a liquid lens, or a similar arrangement. By way of example, the choice of lens type (e.g. C-mount, M12, liquid lens, etc.) can be driven by such factors as lighting/illumination, field of view, focal distance, relative angle of the camera axis and imaged surface, and the fineness of details on the imaged surface. In addition, the cost of the lens and/or the available space for mounting the vision system can drive the choice of lens.
In cameras, it is often desirable to provide an automatic focus (“auto-focus”) capability. By way of example, electro-mechanical autofocus assemblies for photo and video cameras with interchangeable lenses (on a single mounting base) are commonly available. In some conventional photo/video camera auto-focus designs, the focus actuator is integrated in the camera (for example, in most high-end Nikon cameras). While other manufacturers (for example Canon) have integrated the focus motor into the exchangeable lens.
There exist commercially available cameras that employ a built-in auto-focus mechanism and associated drive motor for use with C-mount lenses. Likewise, various cameras have employed an auto-focus mechanism in connection with an M12 lens. However, all these systems are lens-mount specific, in that they are designed to operate with a single type of lens mount. This limits the adaptability of the camera assembly in taking on various tasks, where the ability to select a different type of lens for a specific task can be desirable.
It is therefore desirable to provide a vision system camera assembly that is capable of providing an auto-focus function to a particular type of lens and also allow for the mounting of a plurality of lens types, such as M-12 and C-mount, within the same camera assembly, while avoiding the need of costly changes to the vision system's physical housing or package. This vision system should be able to employ multiple lens types with no reduction in quality of the acquired image when compared with using a system that provides a discrete lens mount for a single lens type. The mechanism should also allow for relatively straightforward change-out of lenses and provide reasonable, long-term reliability in an industrial setting.